System comprising a mass spectrometer coupled to a FAIMS apparatus and methods of operation

A method of operating a system comprising a chromatograph and a mass spectrometer comprises: (a) providing an abundance threshold and a list comprising respective entries for precursor ion species of interest comprising respective precursor-ion m/z ratios; (b) transmitting a first sample fraction portion comprising a plurality of sample-fraction ion species through an ion mobility spectrometer operated in non-dispersive mode to the mass spectrometer; (c) detecting a respective abundance at each of a plurality of sample-fraction m/z ratios; and (d) upon detection of an above-threshold ion abundance at an m/z-ratio corresponding to a first precursor ion species of interest: (d1) inletting a second sample fraction portion into the ion mobility spectrometer operated in dispersive mode such that ions of the first precursor-ion species are preferentially transmitted therethrough; (d2) fragmenting the preferentially-transmitted ions so as to generate product ion species; and (d3) detecting the product ion species.